Conventionally, there has been known a technical idea of successively taking out a plurality of sheets of paper stacked on a chute from the bottom side by use of a pick roller and a separation pad (see, for example, Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2000-143001
Here, the definitions and technical backgrounds of the following terms used in relation to the present invention will be described in order to clarify their comprehensive concepts.
“Regular direction” and “reverse direction” are defined as directions in which an object is moved. In an original-conveyance-type image reader apparatus, “regular direction” is defined as a conveyance direction in which an original sheet supplied to the image reader apparatus is conveyed to pass through an image reading line and is then discharged. Accordingly, the direction of rotation of a pick roller at the time of taking out a sheet of paper stacked on a chute and the direction of rotation of a feed roller for conveying the sheet in the regular direction are defined as the regular rotational direction.
“Reverse direction” is a direction opposite the regular direction. Accordingly, with regard to the rotational directions of the pick roller and the feed roller, a rotational direction opposite the regular rotational direction is defined as the reverse rotational direction.
Similarly, with regard to the rotational directions of a pick motor for imparting drive force to the pick roller and the rotational directions of a feed motor for imparting drive force to the feed roller, drive in the regular direction and drive in the reverse direction are defined on the basis of the above definitions.
FIG. 7 shows an image reader apparatus equipped with a conventional paper feed apparatus described in the above-mentioned Patent Document 1. The illustrated apparatus is an original-conveyance-type image reader apparatus having a housing structure that can be divided into an upper housing and a lower housing. The image reader apparatus has a chute 16, which is provided at the rear and on which an original to be read is stacked, and also has a paper feed apparatus inside the housing. The paper feed apparatus takes out sheets of paper form the chute 16 one sheet at a time, conveys the sheets to reading mechanisms, and discharges them to the outside the apparatus after the sheets are read.
A pick mechanism of the paper feed apparatus shown in a circle of FIG. 7 is formed in the vicinity of a sheet feed port of the chute 16, takes out sheets of paper one sheet at a time, and conveys the sheets to a pair of feed rollers 7. The feed rollers 7 convey each sheet to reading mechanisms (front-face reading mechanism, and reverse-face reading mechanism). Immediately before reaching the reading mechanisms, a leading end of each sheet is detected by means of a detection sensor, and reading operation is started in response to a signal from the detection sensor. Subsequently, when the detection sensor detects a trailing end of the sheet, the reading operation is ended, and the sheet is discharged to an unillustrated stacker by means of discharge rollers 15.
The pick mechanism according to the conventional technique will be further described with reference to FIG. 6, which shows the detail structure of the pick mechanism. As shown in FIG. 6, the pick mechanism includes a pick roller 1, a stopper block 2, a separation pad 3, and a pick arm 4; and provides a function of taking out sheets, one sheet at a time, from a chute on which sheets of paper 5 are loaded.
The pick roller 1 and the stopper block 2 face each other with a proper clearance formed therebetween, so that only a small number of sheets 5 can pass through the clearance. Conveyance of the remaining sheets is prevented, with their leading ends blocked by means of the stopper block 2.
The separation pad 3 is in contact with the pick roller 1. The small number of sheets 5 having passed through the clearance between the pick roller 1 and the stopper block 2 are separated by means of the separation pad 3 in contact with the pick roller 1, so that only a single sheet is conveyed.
The single sheet 5 separated by means of the separation pad 3 further advances, and reaches the feed rollers 7, so that the sheet is conveyed at a conveyance speed of the feed rollers 7.
As described above, the plurality of sheets of paper 5, whose stacking condition on the chute has been corrected by means of the stopper block 2, are pressed against the pick roller 1 by means of the pick arm 4, so that the pick roller 1 generates frictional drive force. Accordingly, when the pick roller 1 rotates in the regular direction, a small number of bottom sheets 5 are taken out and passed through the clearance between the pick roller 1 and the stopper block 2, and advancement of excess sheets is prevented by means of the separation pad 3.